Conventional batteries, whose application is meant to go beyond that of small electronics, are often constructed as hardwired units from a plurality of individual parts, such as cells, for example. At an output, such batteries deliver almost exclusively DC voltage. By contrast, most loads require an AC voltage, with, by way of example, a harmonic voltage profile having a particular frequency, amplitude and phase. Further, the DC voltage is not constant over the state of charge. In order to be able to operate the connected loads and draw the requisite power both at a peak and at an end-of-charge voltage, the loads need to use complex supply circuits. If the voltage required by a load is very different than the voltage provided by the battery, then the power-electronics circuit causes (as a result of what is known as the low modulation index) high losses and high distortions in the output voltage. This relates particularly to the drive of an electric vehicle, which, at low speeds, normally requires AC voltages having a much lower amplitude than the maximum amplitude. The distortions that normally arise as a result of pulse width modulation additionally load an insulation of the motor and therefore affect the life of the motor. On account of variation in the physical and chemical response of the individual battery parts, for example the cells, it is necessary to provide complex monitoring for the battery and, in particular, local charge interchange (what are known as battery management) in order to allow an even state of charge for all battery parts. If just one part of a battery is faulty, for example a cell, then normally the whole battery is unusable. In the case of a vehicle, complete failure of the vehicle must be expected. It may even be necessary for the vehicle or the battery to be actively forced to shut down so that the faulty battery part(s) do not overheat and catch fire when loaded further.
Electric drives in vehicles and also for electric power supply often use two-phase or three-phase AC voltage systems. In order to produce an AC voltage, inverters are used in order to produce the desired AC voltage. These systems, that is to say sources and loads, are normally designed either vis-à-vis a common symmetric reference point (star system) or differentially with respect to one another (delta system). In this case, the voltages arising are normally approximately sinusoidal. However, the number of phases, specifically in motors, defines how finely the circulating field and hence the torque can be controlled. Distortions that are produced by the iron teeth of a stator or a rotor of the electric motor, for example, can be compensated for only to a limited extent. A higher number of phases would have great advantages from the point of view of the motor. A higher number of phases can be produced with known inverters that always produce the voltage against the same reference points, but only with increased complexity.
Usually, three-phase AC motors are used today, in which the profile of the voltage on the three windings is normally offset by 120°. As a result, the windings have a differential voltage in relation to one another. By increasing the number of phases, it would be possible to reduce the differential voltages.
U.S. Pat. No. 6,657,334, which is incorporated by reference herein, describes a combination of an inverter and an electric asynchronous machine that each have more than three phases. In this case, the asynchronous machine has a multiplicity of windings, each winding having two terminals. Each terminal of a winding is individually connected to different phase terminals of the inverter. Each phase terminal of the inverter is connected to two terminals of two different windings of the asynchronous machine in this arrangement. Each winding is thus connected to two phase terminals of the inverter, there being an identical phase shift between the phase terminals.